1. Field of the Invention
The invention concerns a device for implementation and monitoring of thermal ablation of the type having a device for generation of high intensity focused ultrasound and a magnetic resonance system for generation of examination images composed of voxels, which examination images containing temperature information.
2. Description of the Prior Art
Non-invasive temperature determination by means of magnetic resonance thermometry has been used for some time for the monitoring thermal ablation. Examples are radio-frequency ablation, microwave ablation, laser ablation and focused ultrasound. Monitoring of the therapy result in real time during ablations procedures (particularly tumor ablations) is effected by means of MR thermometry, with the therapy being effected with non-invasive high intensity focused ultrasound (HIFU). This ablation method poses special requirements for thermometry. A high temporal resolution is required. To allow prognosis the result of the effected ablation can be implemented, a representation of the treatment region (containing the tumor) with temperature information is provided to the user; the maximum temperature or the temperature curve that is achieved can be shown. The presently used techniques for the application of non-invasive high intensity focused ultrasound enable heating of the area to be treated to more than 80° C. within 5 to 10 seconds. This is dependent on the fact that the examination images generated by means of MR that contain temperature information should be acquired in real time and be updated at intervals of 1 to 2 seconds. A high spatial resolution is additionally necessary. The expansion of the heated region is very slight and corresponds to the size of the HIFU focus. Since the temperature gradients are very steep, significant errors (caused by partial volume effects) occur with regard to the detected temperature when voxels that are too large are used in the MR examination images. The desire for a fast acquisition of the examination images with temperature information thus competes with the desire for high spatial resolution, which makes it difficult to acquire data with sufficient quality and a good signal-to-noise ratio in order exactly measure the existing temperatures.
A device for implementation and monitoring of ultrasound ablations is known from U.S. Pat. No. 5,443,068. Examination images that include temperature information are acquired with a magnetic resonance apparatus. Pathological changes such as tumors can be non-invasively treated with an ultrasound source.
Thermal ablation is also described in “Acoustic Surgery”, Ter Haar, Gail, Physics Today, Vol. 54, Issue 12, pp. 29-34 (2001).